The present application hereby claims priority under 35 U.S.C. Section 119 on European Patent application number 01114599.2 filed Jun. 18, 2001, the entire contents of which are hereby incorporated by reference.
The invention generally relates to a gas turbine with a compressor for air. More particularly, it relates to one which is heated in a plurality of combustion chambers connected in parallel with respect to flow, before it flows via a transfer duct to a gas duct in a turbine. It additionally can relate to a method of operating a gas turbine.
In gas turbines, induced air is usually compressed initially, and is then heated in combustion chambers in order to achieve an economic power density. The hot gas generated in this process then drives a turbine.
In order to achieve good overall efficiency, it is inter alia necessary to keep flow losses small during the guidance of the compressed air. At the same time, however, various components of the turbine installation have to be cooled with the compressed and as yet unheated air. Thus, for example, a transfer or connecting duct, through which hot gas from the combustion chambers flows to the turbine, must be protected from overheating in order to avoid damage.
An arrangement which has widespread application for this purpose is given in FIG. 1 in U.S. Pat. No. 4,719,748. In this arrangement, a long connecting duct between a combustion chamber and a turbine inlet is located directly in an air duct through which compressed air flows to a burner. In this arrangement, no diffuser is shown for air deflection and the flow velocity of the air has fallen greatly on reaching the connecting duct. In consequence, correct cooling is at best possible at relatively low temperatures of the hot gas because higher temperatures require a specific flow velocity both for the compressed air and for the hot gas and a specific air duct height and alignment. As far as can be seen, adequate cooling cannot be achieved with this solution for either the upper side or the lower side of the connecting duct because, on the one hand, the volume of the air duct is very large in this region and because, in addition, both the length of the duct section to be cooled and the distance to be traversed by the compressed air after emergence from a compressor are relatively long.
In addition, however, a complicated cooling device, in which one combustion chamber and a connecting duct leading from this to a turbine are covered by a second wall relative to the flow of the compressed air, is the subject matter of the cited U.S. Pat. No. 4,719,748 in FIGS. 2 to 7 and the associated description. A multiplicity of openings, through which the compressed air is specifically deflected onto the wall sections to be cooled, are provided in this second wall. Although good cooling can be achieved by the variations given for this solution with respect to the number, the size and the shape of these openings, a disadvantage of this arrangement is a not insubstantial, unavoidable pressure loss in the compressed air because the latter must be repeatedly decelerated and accelerated again.
An embodiment of the invention includes an object of creating an arrangement, for a gas turbine, in which an unavoidable pressure loss in the flow of the compressed air is further reduced.
This object may be achieved, for example, by the compressed air flowing with approximately constant velocity over the whole distance in an air duct from the outlet of the compressor to the inlet into the combustion chambers. In this arrangement, the transfer duct may be expediently shorter than the diameter dimension of one of the combustion chambers. This solution is surprisingly advantageous because not only the pressure drop in the air duct but, in addition, a pressure drop in the transfer duct also are lowered to a very small value. In this arrangement, a constant velocity of the air in the air duct may be achieved by the effective cross section of the air duct being almost constant over the whole distance from the outlet of the compressor to the inlet into the combustion chambers.